1. Field of the Invention
The present invention relates to a power amplifier. More specifically, the present invention discloses a power amplifier with constant transconductance.
2. Description of the Prior Art
Power amplifiers are utilized in a wide variety of applications in current electronics technology. Low power consumption is especially important in portable devices.
Unfortunately, the bandwidth of conventional amplifiers must often be substantially reduced to maintain a stable frequency response. Also, there is a trade-off between linearity and power efficiency.
Additionally many analog and digital circuits are often included on the same die. This situation can result in system degradation in the form of power supply noise contamination of the analog signals unless there is sufficient rejection of this noise within the amplifiers in the circuit.
Therefore, there is a need for a more efficient constant transconductance power amplifier which provides improved performance, low power consumption, increased dynamic range, and stable processing characteristics.
To achieve these and other advantages and in order to overcome the disadvantages of the conventional devices in accordance with the purpose of the invention as embodied and broadly described herein, the present invention provides a highly efficient constant transconductance power amplifier with improved performance, low power consumption, increased dynamic range, and stable processing characteristics.
In semiconductor processing it is difficult to maintain consistency from batch to batch. This inconsistency is detrimental to the operational characteristics of the resulting circuitry.
By utilizing an external circuit, for example a resistor circuit, to control the biasing status or level, biasing is kept independent of semiconductor processing. Therefore, variations in processing do not affect circuit biasing thereby maintaining circuit stability.
Transconductances are a very important parameter that must be stabilized in circuits. Transistor transconductances are matched to the conductance of a resistor. Therefore, transistor transconductances are independent of power-supply voltage as well as process and temperature variations.
The present invention comprises a combination of transconductance and constant biasing technology to overcome the drifting problems associated with manufacturing processing. Utilization of the present invention allows these problems to be controlled to within a 10% tolerance range thereby increasing yield rates and lowering manufacturing costs.
An objective of the present invention is to maintain a constant and stable transconductance for stabilization. The transistor transconductances are selected to match the conductance of a resistor. Therefore, the transistor transconductances are independent of supply voltages as well as process and temperature variations.
The transconductance is determined by geometric ratios. It is independent of power supply voltages, semiconductor processing parameters and temperature characteristics. Therefore, the transconductance is not dependant or affected by any parameters with large variability.
Since transistor currents derive from the same biasing network and geometry determines the current rations, all transconductances are stabilized.
The invention combines the above constant transconductance amplifier and current switching technique to achieve the purpose of saving power consumption.
The basic elements of the constant transconductance power amplifier are an error amplifier, an error amplifier, a current source, a current source, a differential current controller, a differential current controller, a current source, a current source, and a constant gm biasing circuit.
The error amplifiers are used with deliberate offset voltages in order to make two transconductance amplifiers which serve in the positive and negative cycle in order to turn on in the appropriate cycle properly.
Positive current sources are current outputs while negative current sources sink the current. The current sources provide current to the current controllers.
The differential current controllers control the amount of current from the current source flowing to the load. This is proportional to the differential input signal.
The constant transconductance biasing circuit provides the transconductance amplifiers with stable biasing voltage. This eliminates any drift associated with process variation.
Providing the offset voltages into the two amplifiers, all transistors are turned off in the quiescent state. The current controllers try to equalize which produces a similar voltage therefore ratioing the currents.
An embodiment of the present invention also provides quiescent current control and reduces excess phase shift which may be introduced into the system by the amplifiers.
These and other objectives of the present invention will become obvious to those of ordinary skill in the art after reading the following detailed description of preferred embodiments.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.